Along with the development of the radio communication service, the users are more and more demanding on the service quality and category, which gives rise to many value-added services. These services bring convenience to people's life and, at the same time, meet their diversified demands.
At present, in a multimedia session, two parties of the ongoing session are allowed to increase the media stream, for example, when a conversation goes on, the video phone becomes possible by adding the video media stream.
The existing method for adding the media stream of multimedia session includes the following:                A first user equipment (UE1) establishes a multimedia session with a second user equipment (UE2).        The UE1 sends a new media stream adding request to the UE2.        The UE2 accepts the adding request;        The added media stream is transmitted between the UE1 and the UE2.        
It is understandable that the interacting of the messages between the UE1 and the UE2 needs to pass through the call control equipment.
During the research and implementation of the prior art, the inventor finds the following drawbacks:
Although the above mentioned method of adding the media stream may realize adding a media stream during the multimedia session, the adding of the media stream is between the two parties of the session and a third user equipment (UE3) cannot be added to receive and transmit the added media stream. In the real situation, however, it is very likely that one user owns more than one UE, each having its own strong points. For example, one user owns two UEs at the same time; one is good in voice quality, but does not support video or supports but with a poor effect, while the other has powerful video function, but is poor in voice quality. If the existing method is adopted to add the media stream, the respective strong points of the two UEs cannot be brought into play. This limitation brings inconvenience to users of the multimedia service and makes it impossible to meet users' requirements on diversified multimedia service.